A conventional ventilator of this kind for use with an internal combustion engine is disclosed in U.S. Pat. No. 3,144,011. As shown in FIG. 1, this ventilator 10 consists basically of a housing 12 and a diaphragm 11 that divides the interior of the housing into a pressure chamber 13 and an atmospheric chamber 14. The pressure chamber 13 is in communication with a crankcase via an inlet port 15. The atmospheric chamber 14 is in communication with an atmospheric source via an atmospheric port 16. An outlet tube 17 extends vertically within the pressure chamber 13, and is in communication with an intake manifold via an outlet port 18. The outlet tube 17 is opened or closed by a valve 19 fixedly secured to the diaphragm 11. The quantity of blowby gas that is introduced into the outlet tube 17 from the pressure chamber 13 can be controlled by the valve 19.
In the aforementioned prior art ventilator for an internal combustion engine, the blowby gas from the crankcase is forced into the intake manifold through the ventilator. To prevent lubricating oil added to the blowby gas from entering the intake manifold, the blowby gas in the crankcase is directed into the pressure chamber 13 of the ventilator 10 via an oil separator, which, as well known in the prior art, acts to separate oil component from lubricating oil added to the blowby gas. However, it is difficult to completely separate oil component with an oil separator. Hence, blowby gas containing oil component left unseparated intrudes into the pressure chamber 13 of the ventilator. When the valve 19 is open, this gas still containing the oil component is admitted to the intake manifold through the outlet tube 17.
When the oil separator separates oil component incompletely in this way, all the oil component introduced into the ventilator will intrude into the intake manifold, increasing the quantity of lubricating oil consumed. Further, the engine becomes contaminated and, therefore, various sensors and other devices installed on the manifold are contaminated, resulting in their malfunction.